In production of light-sensitive materials, it is well known to expand the sensitive wavelength range of silver halide photographic emulsions, namely, to carry out spectral sensitization. Of the spectral sensitization techniques, sensitization of the green wavelength range is important in relation to the fact that eyes of man are very sensitive to light of green wavelength range, because the maximum of luminosity of man is about 545 nm.
It has been well known that addition of a certain kind of benzimidazolocarbocyanine dye is very effective as a means of increasing green sensitivity of silver halide. In this case, the dye added to the silver halide photographic emulsion is adsorbed in silver halide grains in the emulsion to add a longer wavelength absorption zone to the intrinsic absorption zone of silver halide. Namely, spectral sensitization is carried out by the dye.
These techniques have been described in, for example, U.S. Pat. Nos. 2,912,329 and 2,739,149 and British Pat. Nos. 654,690 and 815,172, etc.
However, when benzimidazolocarbocyanine dyes known hitherto are used, an increase of fog is caused under a high temperature or a high temperature and a high humidity after application of the emulsion or stability to the passage of time after application of the emulsion is inferior to cause remarkable reduction of sensitivity. Improvement of these drawbacks of the benzimidazolocarbocyanine dyes, namely, increase of fog under a high temperature or under a high temperature and a high humidity or reduction of sensitivity with passage of time, is one of important subjects in techniques of production of light-sensitive materials.